This application claims the priority German patent document 199 47 408.7, filed Oct. 1, 1999, the disclosure of which is expressly incorporated by reference herein.
The invention relates to an automatic headlight leveling system for a motor vehicle.
Dynamic headlight leveling helps to improve traffic safety, since it eliminates the need for the driver to carry out a manual operation, which would have to take place as a function of the vehicle load. When headlights with an improved luminous power are used, for example, by means of electric discharge lamps, the dynamic headlight leveling additionally prevents the projection of glare onto oncoming traffic. This applies also to dynamic operations, as, for example, considerable acceleration.
An automatic headlight leveling system of this type is described, for example, in the ATZ article xe2x80x9cDynamic Automatic Headlight Levelingxe2x80x9d, 9/1992, Page 466, and on, in which compression of the vehicle springs (which has the effect of a longitudinal inclination or pitch of the vehicle body), is detected by two ultrasonic level sensors which are offset in the longitudinal direction. After measurement, the pitch angle of the vehicle body will be manifested in the form of a level difference. (In this case, the level sensors measure the levels or distances between the vehicle body and the road in the front and in the rear on the vehicle body floor. Level sensors are also used in the form of axle sensors which each measure the level or the distance between the vehicle body and the front and rear vehicle axles). In an electronic control unit having a microcomputer, the desired value for the headlight adjustment, such as the position of a stepping motor to be adjusted, is computed as a function of the measured level difference. The level difference is averaged over a time period which is a function of the vehicle speed.
The known dynamic automatic leveling system differentiates between a slow (static) and a fast (dynamic) control mode. In the slow automatic control mode, the comparatively long-lasting or static pitch angles (longitudinal inclinations) which are generated particularly by the loading of the vehicle, the emptying of the tank and/or the change of the aerodynamic drag are taken into account. In the fast automatic control mode, the changes of the pitch angle as a result of driving-dynamics-related influences (particularly, acceleration or deceleration operations) are taken into account.
In order to avoid stressing the stepping motor in the headlights too long, rapid automatic control mode will be switched on only when a considerable pitch angle change due to driving-dynamics-related influences is to be expected. For this purpose, the first derivative of the vehicle speed signal and/or the brake light signal are analyzed. In view of the actual pitch angle changes, these signals supply only limited information. Furthermore, a control as a function of these signals takes place only in a delayed manner.
One object of the invention is to provide an improved system for an automatic leveling control of the type described above, which avoids the disadvantages of the prior art, under dynamic driving conditions, and at the same time achieves an optimal illumination of the road.
Another object of the invention is to provide a headlight control system that minimizes glare that is directed at the oncoming traffic.
These and other objects and advantages are achieved by automatic headlight leveling system according to the invention, which has two level sensors that are offset in the longitudinal direction for measuring the vehicle body pitch angle in the form of a level difference, and an electronic control unit for determining the desired value for the headlight adjustment as a function of the measured level difference. The control unit determines the desired value as a function of the first derivative of either the directly measured level difference or a further processed level difference. The term xe2x80x9cdirectly measured level differencexe2x80x9d indicates particularly the difference of the level values measured by the level sensors and supplied in the form of measuring signals to the control unit. The term xe2x80x9cfurther processed level differencexe2x80x9d indicates particularly the difference of the measured level values and/or the level values further processed in the control unit and/or the further processed difference of the measured or further processed level values. Further processing may be, for example, an averaging or another filtering, and may also be another elimination of interfering influences.
By analysis of the first derivative of the level difference, it is determined whether and to what extent a change of the pitch angle actually exists. This permits a more direct automatic pitch angle control. Based on the magnitude of the first derivative, it can, for example, be decided whether a slow or fast automatic control mode is to be selected.
In an advantageous embodiment of the invention, the time period for averaging of the measured level difference is defined as a function of the first derivative of the measured level difference.
In another embodiment of the invention, a static level difference value is determined at least by averaging the directly measured level difference for a first time period; and a dynamic level difference value is determined at least by averaging the directly measured level difference for a second time period. The first time period is defined to be significantly longer than the second time period. The desired value is defined as a function of the first derivative of the dynamic level difference value as the further processed level difference. As a result, the pitch angle deviation due to both static and dynamic influences can be carried out simultaneously. The pitch angle changes due to static and dynamic influences are considered separately, and their mutual interaction can also be taken into account.
The desired value is preferably determined also a function of the second derivative of the dynamic level difference value. By adding vehicle-relevant quantities (such as the position of the center of gravity, moments of inertia, spring rates, etc.), automatic control can be carried out as a function of a predictable pitching movement. This permits a further acceleration and improvement of the control.
In another advantageous embodiment of the invention, the desired value is determined also as a function of additional information transmitted to the control unit (which information is preferably already available from other systems in the vehicle). Such information may, for example, be road information from a navigation system, distance from a preceding vehicle from a ranging system, accelerator pedal position, brake pressure, vehicle speed and/or the visual range of a fog sensor. As a result, a very good situation-adapted intelligent control of the headlight inclination can be carried out.
GPS data, for example, can be used in conjunction with a navigation system in the motor vehicle concerning the type of road (for example, turnpike or city street). The control unit can thereby always implement a comparatively more raised headlight adjustment for turnpikes than for city streets. By means of the level course information of the GPS data and of the navigation system, humps and troughs can be better illuminated.
Furthermore, the current distance from a preceding or an oncoming vehicle can be transmitted, for example, by an ACC system (adaptive cruise control) in the motor vehicle to the control unit. In this case, a lowering of the headlights can always take place for limiting glare.
The position of accelerator pedal or of the throttle valve can be taken into account in order for example, to carry out a preventive lowering of the headlights in the event of an expected elevation of the front wheels as a result of an acceleration operation.
Likewise, the brake pressure or the speed of the change from the accelerator pedal to the brake pedal can be analyzed in order to preventively raise the headlights, for example, in the event of an emergency braking, for improving the visibility.
Finally, the signal of a range-of-vision sensor or fog sensor can also be analyzed in order to preventively lower the headlights in dense fog for minimizing the scattered-light density.
The invention permits more direct, more precise and faster control of the headlight inclination than the prior art.